@mixin beveled-corners($bg, $tl:0, $tr:$tl, $br:$tl, $bl:$tr) {
    background: $bg;
    background: linear-gradient(135deg, transparent $tl, $bg 0) top left, linear-gradient(225deg, transparent $tr, $bg 0) top right, linear-gradient(-45deg, transparent $br, $bg 0) bottom right, linear-gradient(45deg, transparent $bl, $bg 0) bottom left;
    background-size: 50% 50%;
    background-repeat: no-repeat;
}

div {
    @include beveled-corners(#58a, 15px, 5px);
}